Fluid–structure interaction simulations to investigate the asymmetrical pattern and energy transfer during vocal fold vibrations

Asymmetrical vocal fold vibration is the cause of many voice problems. In this study, a two-dimensional fluid–structure interaction model is developed with the finite element method in COMSOL Multiphysics. The vocal folds with asymmetric stiffness are simulated and compared with the symmetric vocal folds as well as unilateral immobile vocal folds. The vocal fold vibration pattern and energy exchange between the fluid and vocal fold structure are analyzed. The results show that the unilateral vocal fold paralysis (UVFP) and the stiffness difference between the two vocal folds would lead to a decrease in the vibration amplitude compared with symmetrical conditions. The asymmetrical vocal fold vibration allows a frequency lock-in between two sides of the vocal fold, and the lock-in frequency is sensitive to the vocal fold stiffness. The vocal fold vibration can maintain a quasi-periodic pattern when the stiffness difference is less than 5 MPa. 10 MPa stiffness difference can trigger a transition from the quasi-periodic state to the chaotic state. The energy conversion efficiency between fluid and structure is reduced in the presence of a stiffness difference and under UVFP conditions. This efficiency is further decreased when chaotic vibration happens, indicating the importance of vibration regularity in maintaining effective fluid-to-structure energy transfer.